Semiconductor processing temperature control

ABSTRACT

A temperature control system having a re-circulation loop that uses valves to selectively circulate a temperature control fluid through a cooling system, through a heating system, or through a through passage so as to controlling the temperature of the temperature control fluid, which, in turn, controls the temperature of a target. A temperature sensor monitors the target&#39;s temperature. A controller controls valve operation in response to the temperature measured by the temperature sensor to obtain a predetermined target temperature. Beneficially, the controller controls the target&#39;s temperature according to a predetermined temperature profile. Continuous etching along a predetermined temperature profile is possible.

BACKGROUND OF THE INVENTION

This application is a divisional of prior application Ser. No.10/983,248, filed Nov. 8, 2004, which is a continuation of priorapplication Ser. No. 10/097,603, filed Mar. 15, 2002, now U.S. Pat. No.6,822,202.

FIELD OF THE INVENTION

The present invention relates to semiconductor processing temperaturecontrol. More specifically, it relates to controlling the temperature ofa semiconductor processing device (target) using a temperature controlfluid that is selectively heated and cooled. The temperature of thesemiconductor processing device (target) is variable over time accordingto a predetermined temperature profile.

DISCUSSION OF THE RELATED ART

Semiconductor device manufacturing involves a large number of processingsteps, such as semiconductor crystal growth, wafer cutting, waferpolishing, doping, material depositions, oxide growths, masking, andetching. Because modem semiconductors must be low cost and highlyreliable, rapid fabrication with high device yields and with tighttolerances is critical. That generally requires automated equipment andprocesses in specially designed clean rooms.

While clean rooms are generally successful, they are expensive to buildand operate, with the cost being highly dependent on floor space. Thus,only the processing steps that must be performed in a clean room areusually performed there. Furthermore, it is beneficial to minimize thedevice processing and wafer handling steps required to be performed in aclean room. Many of the steps performed in clean rooms require heatingand/or cooling. For example, since etching is highly temperaturedependent, the etching temperature of each etching step (there might beseveral) must be carefully controlled. Increasing etching difficult isthat as semiconductors get denser, the need for accurate temperaturecontrol becomes greater. Thus, a semiconductor wafer might be etched ata carefully controlled first temperature, then etched at a carefullycontrolled second temperature, and then etched at a carefully controlledthird temperature, and so on.

In prior art semiconductor processing, multiple etchings typicallyrequired the semiconductor wafers being processed to be moved betweendifferent etching vessels that are maintained at different temperatures.This increased the risk of wafer contamination, necessitated multipleetching vessels and temperature control systems, increased processingtime, and increased the required clean room floor space. An alternativewas to etch the semiconductor wafers in one vessel at one temperature,remove the semiconductor wafers, change the vessel's temperature,re-insert the semiconductor wafers, and then repeating the process asrequired. Semiconductor wafer removal was required because it was verydifficult or impossible to rapidly change a vessel's temperature, andbecause it was very difficult or impossible to control the temperature'srate of change.

In clean rooms, temperature control is usually achieved by pumping atemperature control fluid through a semiconductor processing vessel,chamber, tool, device, or assembly, all of which are genericallyreferred to hereinafter as targets. The temperature control fluid isusually heated or cooled using a heat exchanger, with heat flow beingdependent on temperature requirements. Typically, electricallycontrolled valves are used to adjust the control fluid's flow through aheat exchanger. Thus, prior art semiconductor process temperaturecontrols use various types of pipes, pumps, thermostats, heatexchangers, temperature controllers, refrigeration units, heaters,valves, and temperature control fluids.

While beneficial, prior art semiconductor process temperature controlsusually either cooled or heated targets, but not both. Systems that bothheated and cooled usually used separate temperature control fluids. Thatis, a fixed volume of temperature control fluid was used for heating,while another fixed volume was used for cooling. Such systems requiredmultiple circulation pipes through the targets, which increased cost andreduced reliability.

However, U.S. Pat. No. 6,026,896 discloses a semiconductor processtemperature control system in which control valves switch thetemperature control fluid that passes through the target (reference FIG.3, valve 74, and the supporting text of U.S. Pat. No. 6,026,896). U.S.Pat. No. 6,026,896 thus teaches selectively controlling the temperaturecontrol fluid (heated or cooled) that flows through the target. Whilethe system disclosed in U.S. Pat. No. 6,026,896 is beneficial, multiplepumps, numerous control valves, and extensive piping are still required.Furthermore, temperature adjustment and regulation requires rapid valveswitching and flushing of the temperature control fluid. This candetrimentally impact reliability because of thermal stresses andpressure mismatches between the heating and cooling subsystems.Furthermore, mass mixing between the heated and cooled temperaturecontrol fluids leads to increased power consumption because previouslyheated temperature control fluid must be cooled, while previously cooledtemperature control fluid must be heated.

Therefore, a semiconductor temperature process control system that canheat and cool using the same temperature control fluid would bebeneficial. Even more beneficial would be a semiconductor temperatureprocess control system that uses only one volume of temperature controlfluid and that requires only one temperature control fluid pump. Stillmore beneficial would be a semiconductor temperature process controlsystem that uses only one volume of temperature control fluid, that usesonly one temperature control fluid pump, and that has reduced thermalshock and reduced valve switching. More beneficial yet would be anefficient semiconductor temperature process control system that usesonly one volume of temperature control fluid, that uses only onetemperature control fluid pump, and that has low thermal shock andreduced valve switching. Such a system having variable temperatures thatchange according to well-defined temperature profiles (well-controlledrates of temperature change) would be highly beneficial in that suchwould enable continuous etching of a semiconductor wafer at differenttemperatures that change according to a predetermined temperatureprofile.

SUMMARY OF THE INVENTION

The following summary of the invention is provided to facilitate anunderstanding of some of the innovative features unique to the presentinvention, and is not intended to be a full description. A fullappreciation of the various aspects of the invention can be gained bytaking the entire specification, claims, drawings, and abstract as awhole.

Accordingly, the principles of the present invention are directed to asemiconductor process temperature control system that heats and cools atarget using one temperature control fluid. Beneficially, the principlesof the present invention are implemented using a re-circulation loopthat is pressurized by one pump (or one pumping system). The principlesof the present invention can be implemented with low thermal shock andreduced valve switching, and thus with improved reliability.Furthermore, the principles of the present invention can be implementedwith relatively high efficiency.

A semiconductor process temperature control system according to theprinciples of the present invention includes a re-circulation loop forretaining and circulating a volume of temperature control fluid suchthat the temperature control fluid is in thermal communication with atarget whose temperature is being controlled. The temperature controlfluid is circulated through the re-circulation loop by a fluid pump. There-circulation loop includes control valves that selectively enable someof the temperature control fluid to flow through a cooling heatexchanger, through a heating heat exchanger, or through neither heatexchanger. The control valves are controlled by a controller, whichreceives temperature information that is related to the temperature ofthe target from at least one temperature sensor. Based on thetemperature information, some of the temperature control fluid is passedthrough a selected heat exchanger such that the target achieves apredetermined temperature. Beneficially the controller further receivestime information from a timer. In such cases, the controller controlsthe flow of the temperature control fluid such that the temperature ofthe target follows a predetermined temperature profile. This enablescontinuous etching of a semiconductor wafer at different temperaturesthat change according to a well-defined temperature profile.

Beneficially, the re-circulation loop retains a volume of temperaturecontrol fluid such that the temperature control fluid can changetemperatures relatively rapidly. Furthermore, the re-circulation loopbeneficially passes only part of the temperature control fluid through aheat exchanger. This reduces thermal stress and stabilizesre-circulation loop pressures.

Furthermore, the temperature sensor is beneficially located such that itaccurately senses a temperature that is related to the target. To thatend, the temperature sensor beneficially senses the target temperature,the temperature of an object in thermal communication with the target,or the temperature of the temperature control fluid as the temperaturecontrol fluid leaves the target area.

A semiconductor process temperature control system according to theprinciples of the present invention enables beneficial semiconductorprocessing methods. For example, a method of continuously etching asemiconductor wafer includes etching a semiconductor wafer at a firsttemperature, adjusting the etch temperature along a well-definedtemperature profile to a second temperature while continuing to etch,and subsequently etching the semiconductor wafer at the secondtemperature. Beneficially, etching is performed at the first temperaturefor a predetermined time, and then at the second temperature for anotherpredetermined period of time. Furthermore, the etching temperatureduring the temperature adjustment from the first temperature to thesecond temperature beneficially occurs over a predetermined time.

A semiconductor process temperature control system according to theprinciples of the present invention can include multiple individualtemperature control systems that share heating and/or cooling resources.The temperature profiles of a plurality of targets can be controlled. Ofcourse, a plurality of temperature sensors for sensing the temperaturesof the individual targets, a plurality of temperature control units forcontrolling the temperatures of the individual targets, and a pluralityof re-circulation loops for isolating the temperature control fluids forthe individual targets are required. Such re-circulation loops caninclude circulation pumps and control valves.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a schematic diagram of a temperature control system that is inaccord with the principles of the present invention;

FIG. 2 illustrates a temperature profile of a target during etching;

FIG. 3 is a schematic diagram of a temperature control system that is inaccord with the principles of the present invention and that includesmultiple temperature controlled targets; and

FIGS. 4A-4F illustrate a fabrication process that benefits fromtemperature control systems that are in accord with the principles ofthe present invention.

FIG. 5 illustrates a fabrication process that benefits from temperaturecontrol systems that are in accord with the principles of the presentinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Reference will now be made in detail to an illustrated embodiment of theinvention, the example of which is shown in the accompanying drawings.

FIG. 1 illustrates a semiconductor process temperature control system 10that is in accord with the principles of the present invention. Thesemiconductor process temperature control system 10 both heats and coolsa target 12, as required, using a temperature control fluid in are-circulation loop 14. The re-circulation loop 14 includes a throughpassage 16, a cooling passage 18, and a heating passage 20. Thetemperature control fluid is pumped through the re-circulation loop 14by a pump 22.

Still referring to FIG. 1, the through passage 16, the cooling passage18, and the heating passage 20 are in parallel. They meet at a firstbranch 24 and at a second branch 26. The through passage 16 transportssome of the temperature control fluid directly from the first branch 24to the second branch 26. The cooling passage 18 includes a cooling valve28 and a cooling heat exchanger 30 that is cooled by lines 31 thattransport a refrigerated cooling fluid. The cooling valve 28 iselectrically operated under the control of a controller 32. The heatingpassage 20 includes a heating valve 36 and a heating heat exchanger 38.The heating heat exchanger receives power or heat on lines 39. Forexample, the lines 39 might be electrical wires that supply power to aresistive heat source in the heating heat exchanger 38, or the lines 39might transport a heated fluid through the heating heat exchanger. Theheating valve 36 is also electrically operated under the control of thecontroller 32.

The controller 32 receives temperature information from at least onetemperature sensor 40. That temperature sensor is in thermalcommunication with the target 12 such that target temperatureinformation is available to the controller 32. The temperature sensor 40could be in direct thermal contact with the target 12, in thermalcontact with a material in or on the target, or in thermal contact withthe temperature control fluid, beneficially as the temperature controlfluid leaves the target area. More than one temperature sensor 40 cansupply information to the controller 32.

In operation, the controller 32 is programmed to set the temperature ofthe target 12 at predetermined temperatures at predetermined times, withthe temperatures always being greater than the lowest temperatureachievable from the cooling heat exchanger 30, but always less than thehighest temperature achievable from the heating heat exchanger 38. Ifthe temperature information from the temperature sensor 40 shows thatthe target temperature is less than the programmed temperature at theparticular moment in time, the controller 32 opens the heating valve 36.This enables some of the temperature control fluid to flow through theheating heat exchanger 38, which heats the temperature control fluid.That heated temperature control fluid then mixes with the temperaturecontrol fluid that passes through the through passage 16, thus causingthe temperature of the temperature control fluid to rise. This causesthe target temperature to rise. When the target temperature is correct,the controller 32 closes the heating valve 36.

Alternatively, if the temperature information from the temperaturesensor 40 shows that the target temperature is greater than theprogrammed temperature at the particular instant, the controller opensthe cooling valve 28. This enables some of the temperature control fluidto flow through the cooling heat exchanger 30, which cools thetemperature control fluid. That cooled temperature control fluid mixeswith the temperature control fluid that passes through the throughpassage 16, thus causing the temperature of the temperature controlfluid to drop. This causes the target temperature to drop. When thetarget temperature is correct, the controller 32 closes the coolingvalve 28.

The controller 32 beneficially proportionally controls the temperature.That is, if a desired temperature is far from the measured temperature,the controller 32 causes significant heating or cooling. Then, as thecurrent temperature approaches the desired temperature the rate ofheating/cooling decreases.

Furthermore, the controller 32 beneficially can be programmed such thatthe target temperature changes over time according to a predeterminedtemperature profile. This is extremely beneficial in some applications.For example, FIG. 2 illustrates a desired temperature profile of atarget in which (or by which) a semiconductor wafer is being etched.Assume that the semiconductor wafer is to be etched at different ratesat different times using the same etchant. Further assume, as is usuallythe case, that the etch rate is temperature dependent. At time 0, thesemiconductor process temperature control system 10 sets the target 12at a first temperature, say 80° C., which induces a desired first etchrate. After a time T1, the etch rate ideally should be at a secondtemperature, say 40° C., which induces a second etch rate. As aninstantaneous temperature change is not possible, shortly before time T1(at say T1−) the controller 32 begins adjusting the flow of thetemperature control fluid in a controlled manner through the coolingvalve 28. This controlled adjustment enables a repeatable temperaturechange profile. This enables the etch process designer to implement acontinuous etch system having known etch characteristics along atemperature change. After some temperature adjustment time, say at timeT1+, the target temperature is at the second temperature and etchingcontinues at the second etch rate.

Later, say at time T2, the etch rate should changes to a third rate.Shortly before time T2 (at say T2−) the controller 32 begins adjustingthe flow of the temperature control fluid in a controlled manner throughthe cooling valve 28. This adjusts the target temperature along apredetermined and repeatable temperature profile curve to a thirdtemperature, say 20° C., which induces a third etch rate. After sometemperature adjustment time, say at time T2+, the target temperature isat the third temperature. Finally, at a later time, say at time T3, theetch rate should change back to the first rate. Then, shortly beforetime T3 (at say T3−) controller 32 begins adjusting the flow of thetemperature control fluid in a controlled manner through the heatingvalve 36. This adjusts the target temperature along a predetermined andrepeatable temperature profile curve back to the first temperature.After some temperature adjustment time, say at time T3+, the targettemperature is back at the first temperature. To assist ease ofoperation, and to enable changes in the temperature profiles, thecontroller 32 beneficially operates under software control. An exampleof an etch process that benefits from continuous etching along acontrolled temperature profile is provided subsequently.

Turning back to FIG. 1, the blending of heated/cooled temperaturecontrol fluid with temperature control fluid that passes through thethrough passage 16 enables both heating and cooling with the sametemperature control fluid. Furthermore, sharp thermal shocks andpressure disturbances are avoided. Additionally, the closedre-circulation loop 14 minimizes the volume of temperature control fluidthat must be heated and cooled to change the temperature of the target12. This enables relatively rapid temperature changes, which can beimportant in applications like that described above with reference toFIG. 2 (and subsequently described with reference to FIGS. 4A-4F).Additionally, only one pump (or pump system) is required for bothheating and cooling. Another benefit of the semiconductor processtemperature control system 10 is that rapid switching of the valves 28and 36 are not required to maintain a fixed temperature. That is, ifboth valves are closed the only temperature control fluid that iscirculated is through the through passage 16. If that temperaturecontrol fluid is at or near the desired fixed temperature, cyclingbetween heating and cooling is not required.

FIG. 3 illustrates a multiple target temperature control system 100 thatis in accord with the principles of the present invention. The targettemperature control system 100 is essential comprised of paralleledtemperature control systems 10. However, the temperature control system100 can control the temperatures of multiple targets 12. Each target hasits own re-circulation loop 14 with through passage 16, cooling passage18, and heating passage 20. Furthermore, each target 12 has anassociated volume of temperature control fluid that is pumped throughthe target's associated re-circulation loop 14 by a pump 22.Additionally, each re-circulation loop 14 includes a first branch 24, asecond branch 26, a cooling valve 28, a cooling heat exchanger 30 cooledby lines 31, and a heating valve 36. However, the temperature controlsystem 100 beneficially includes a single heat exchanger 38 and a singlecooling source 50. As shown, each target 12 also has an associatedtemperature sensor 40 that feeds temperature information to atemperature control unit 32. There might be one temperature control unit32 or multiple temperature control units.

Still referring to FIG. 3, the cooling heat exchanger 50 cools arefrigerated cooling fluid in lines 31. The refrigerated cooling fluidin lines 31 subsequently cool fluids in the individual re-circulationloops 14 (a set for each target) via cooling heat exchangers 30.Similarly, the heat exchanger 38 heats the heating fluids in each of theindividual re-circulation loops 14.

It is more economical to locate as much of each temperature control unitas possible outside of the clean room. Thus, FIG. 3 shows much of theheating and cooling units being located in a utility room 64, which isbeneficially outside of clean rooms that house the targets 12.

As previously noted, the temperature control units 10 and 100 are highlybeneficial in that they enable continuous etching of a target 12 as thetarget's temperature is adjusted in accord with a predeterminedtemperature profile. This enables a new level of semiconductorfabrication performance. For example, FIG. 4A through 4F illustrate aspecial contact formation process that benefits from the principles ofthe present invention. The process begins with a structure as shown inFIG. 4A. That structure includes a copper plug 44 embedded in a siliconlayer 42. Over the copper plug 44 and silicon layer 42 is a firstnitride layer 46. Over the first nitride layer 46 is a first polyimidelayer 48, which is capped by a second nitride layer 52. Over the secondnitride layer 52 is a second polyimide layer 54, which is capped by ametal hardmask 56.

Referring now to FIG. 4B, processing begins by depositing a resist layer58 on the metal hardmask 56 at a temperature of 40° C., and then byetching the resist layer 58 to form an opening 60. Turning now to FIG.4C, after the opening 60 is formed, the opening is driven toward thecopper plug 44. First, the temperature of the structure is changed to50° C. and an aperture is formed through the metal hardmask 56. Thisremoves the remaining photoresist 58. Then, the temperature is adjustedto 40° C. and the second polyimide layer 54 is etched. Then, thetemperature is adjusted once again to 50° C. and the second nitridelayer 52 is etched. Then, the temperature is adjusted once again to 40°C. and the first polyimide layer 48 is etched. Finally, the temperatureis adjusted once again to 50° C. and the first nitride layer 46 isetched. This exposes the copper plug 44. It should be noted that etchingis continuous, with only the etch temperature being changed.

Referring now to FIG. 4D, another photoresist layer 68 is then depositedon the exposed portion of the copper plug 44 and on the exposed portionof the metal hardmask 56. The photoresist layer is then patterned towiden expose part of the metal hardmask 56 adjacent the opening 60.Next, referring to FIG. 4E, the temperature of the structure is raisedto about 40° C. and the photoresist layer 68 is removed. This results inexposed top portions of the metal hardmask 56 and of the second nitridelayer 52. Then, the temperature of the structure is changed to roomtemperature. Referring now to FIG. 4F, copper is then electroplated intothe opening 60 to form the now finished contact 44.

It should be noted that all the foregoing processes are implementtemperature selective etching. Furthermore, all etching performed withreference to FIG. 4C is performed continuously.

The embodiments and examples set forth herein are presented to bestexplain the present invention and its practical application and tothereby enable those skilled in the art to make and utilize theinvention. Those skilled in the art, however, will recognize that theforegoing description and examples have been presented for the purposeof illustration and example only. Other variations and modifications ofthe present invention will be apparent to those of skill in the art, andit is the intent of the appended claims that such variations andmodifications be covered. The description as set forth is not intendedto be exhaustive or to limit the scope of the invention. Manymodifications and variations are possible in light of the above teachingwithout departing from the spirit and scope of the following claims. Itis contemplated that the use of the present invention can involvecomponents having different characteristics. It is intended that thescope of the present invention be defined by the claims appended hereto,giving full cognizance to equivalents in all respects.

1-22. (canceled)
 23. A method of forming a contact comprising: providinga silicon layer with a copper plug embedded therein; providing a metalhardmask over the copper plug; depositing a resist layer over the metalhardmask; a first etch step for etching a first opening in the resistlayer at a first temperature; and a second etch step for etching themetal hardmask at a second temperature wherein the same etchant is usedfor the first etch step and the second etch step.
 24. A method offorming a contact according to claim 23, wherein the first temperatureand the second temperature are different.
 25. A method of forming acontact according to claim 23, wherein the first and second etch stepsare continuously performed in one vessel.
 26. A method of forming acontact according to claim 23, further comprising completely removingthe resist layer during the second etch step.
 27. A method of forming acontact according to claim 23, further comprising sequentially providinga first nitride layer, a first polyimide layer, a second nitride layer,a second polyimide layer, before providing said metal hardmask.
 28. Amethod of forming a contact according to claim 27, further comprisingsequentially and continuously etching the second polyimide layer, thesecond nitride layer, the first polyimide layer and the first nitridelayer to form an opening to expose said copper plug.
 29. A method offorming a contact according to claim 27, wherein the first polyimidelayer and the second polyimide layer are etched at said firsttemperature.
 30. A method of forming a contact according to claim 28,wherein the first nitride layer and second nitride layer are etched atsaid second temperature.
 31. A method of forming a contact according toclaim 29, wherein the second polyimide layer, the second nitride layer,the first polyimide layer and the first nitride layer are etched in thesame vessel and using the same etchant.
 32. A method of forming acontact according to claim 30, further comprising electroplating copperin said opening.